Electrolytic apparatus



W. E. GREENAWALT.

ELECTROLYTIC APPARATUS.

APPLICATION FILED JAN. 1, 1919.

Patented Sept. 28,1920.

2 SHEETS-SHEET I.

IN I/EIV TOR PATENT OFFICE.

WILLIAM E. GREENA\VALT, OF DENVER, COLORADO.

ELECTROLYTIC APPARATUS.

Specification of Letters Patent.

Patented Sept. 28, 1920.

Application filed January 7, 1919. Serial No. 270,046.

To all whom it may concern Be it known that I, \VILLIAM E. GREENA- \VALT, a citizen of the United States, residing in the city and county of Denver and State of Colorado, have invented certain new and useful Improvements in Electrolytic Apparatus, of which the following is a specification.

The invention has for its more immediate object the effective application of sulfur dioxid, as a depolarizer and reducing agent, in the electrolysis of impure copper solutions, especially solutions obtained from leaching ores and containing salts of iron.

This application may be regared as a continuation in part, of that shown in my process applications, Serial Numbers, 812,951, filed Jan. 19, 1914., and 185,652, filed August 11, 1917, and my apparatus applications, Serial Numbers 845,011, filed June 13, 191 i; 16,962. filed March 25, 1915; and li5,884=, filed February 1, 1917.

The application of sulfur dioxid to an electrolyte, to act either as a depolarizer or as a reducing agent for the ferric salts formed by the electrolytic action, presents some very serious difficulties. These may be briefly summarized as follows:

Sulfur dioxid is only slightly soluble in water or'in copper solutions. It has a very low solubility in hot solutions. As a reducing agent for ferric salts it acts quite slowly in cold solutions. It reacts fairly satisfactorily in hot solutions. lVhether cold or hot, the solubility of the sulfur dioxid is so small that if a copper solution at ordinary temperatures is electrolyzed. the sulfur dioxid is quickly consumed, and the deleterious effect of the ferric salts soon becomes evident. A copper solution, in which the iron is reduced, or in the ferrous condition, can be electrolyzed with a cathode ampere efficiency closely approximating 100%. As soon, however, as ferric salts are formed, the efficiency drops in proportion to the amount of ferric salts in the electrolyte. Even as low as 0.25% ferric iron in the electrolyte exerts a very deleterious effect. In good electrolytic work in the deposition of copper from impure solutions. the amount of ferric iron in the issuing solution should not exceed 0.25%. It should be less. It is usually considerably more-in some instances in commercial plants, it is as high as 1.0%. Agitation, or rapid circulation, is desirable in copper deposition, but

agitation or rapid circulation is incompatible with effective application of sulfur dioxid to the electrolyte, in the electrolyzer, as ordinarily applied.

In my present apparatus it is possible to get a good effect of the sulfur dioxid absorption and reduction, as also a good effect in the electrolysis, due to the continuous ap plication of the gas to the electrolyte, and the rapid circulation of the electrolyte made possible by this apparatus.

As electrolytic copper extraction plants are usually operated, the copper solution from the leaching vats is passed through a scrubbing tower against the ascending sulfur dioxid gas. This reduces much of the iron and usually provides for a small temporary excess of the gas in the liquid. The excess of the gas is usually only temporary, especially if a considerable interval of time elapses between the application of the gas and the electrolysis of the liquid. The excess gas, on storing of the liquid, combines with constituents in the li uicl capable of combining with it, such as ferric salts, and thus the free gas is eliminated before the liquid is electrolyzed, and then there is no restraining effect on the formation of the ferric salts in injurious amounts duringelectrolysis. To maintain the solution reduced, or to provide for a continuous excess of the gas in the electrolyte, it would be necessary to return the solution to the gas towers for momentary contact, and this would be a serious undertaking, so serious that it apparently has never received prac-' tical application.

In my present apparatus the gas is confined over a pool of the liquid, or electrolyte, in a reducing chamber, or reducer, which communicates with the electrolytic tank, and the electrolyzer and reducer are so arranged that there is a continuous flow from one to the other, and so that the liquid in the reducing chamber is treated with the gas while another portion of the liquid is subjected to electrolysis. The reducing chamber and electrolyzer are so arranged in relation to one another that there is a voluminous flow of electrolyte between the electrolyzer and reducer in a sort of closed circuit, while at the same time there is a progressive advance of a portion of the electrolyte through the electrolyzers composing the series for complete electrolytic treatment. T is gives a much desired. "very same time a portion of the liquid is rapid circulation of the electrolytein contact With the electrodes to act as a depolarizer and to obtain a high ampere eiliciency.

in the deposition of the copper. it is also possible, in this Way, to maintain the ferric salts at a low standardso low it is believed as not to seriously interfere with the realization of an almost theoretical amp re efficiency.

The apparatus may be more particularly described by referring to the accompanying drawings, in which Figure 1 represents a transverse section through an electrolytic unit consisting of electrolyzers and reducer; Fig. 2, a corresponding ideal longitudinal section, and Fig. 3 a diagrammatic plan flow sheet of a complete installation. in Fig. 2 the electrolyzer and the pipe connect ing the electrolyzer with the gasing :hamher are supposed to be rotated at right angles from their true position in order to clearly show the relation between the electrolyzer and the gasing chamber.

In the drawings, E shows an electrolytic tank containing a portion of the electrolyte and the electrodes, in which 1 are the anodes and 2 the cathodes. ll is a reducing chamber, composed of a lower portion 3 adapted to contain a portion of the liquid, or electrolyte, and a removable upper portion 4 adapted to confine a over the liquid in the lower aortion. The lower portion of the reducing chamber is arranged so that there may be a continuous circulation of the liquid from the reducer to the electrolyzer B, through the pipe A, and a return flow from the electrolyzer to the reducer through the pipes B and C, While at the passed to the next electrolytic unit consisting of electrolyzers and corresponding reducer,

through the pipe D. The cover, or upper portion of the reducer, is provided with a gas inlet 5 and a gas outlet 6, by means of which a gas is introduced. into the reducer from gas generator, and confined over the liquid, and the excess is passed on, by means of an exhauster, to the reducer of the next electrolytic unit.

lVithin the reducing chamber is a s "ay ing device by means of which the liquid is sprayed into the gas confined over it to promote the desired chemical reactions, and may conveniently consist of perforated dislrs 7 mounted on a shaft 8, and when rapidly rotated by the motor 9, the disks spray the liquid into the confined over it and at the same time submerge some of the gas in the liquid. Alternating with the disks are stationary plates, or baliles, 10, preterably perforated, to entrain some of the in the liquid, and to make a more effective mix-- ing of the and liquid.

At one end of the reducing chamber is a trough 11, adapted to maintain a portion of the liquid at a higher lever than the general level of the liquid in either the reducer or electrolyzer, and is supplied With liquid by the spray induced by the rapidly rotating disks. This difference of liquid level in the trough ll is used to maintain a flow of the liquid from the reducer to the electrolyzer through the pipe A and a return flow from the electrolyzer to the reducer through the pipes B and C. It is also desirable to have a progressive flow of the liquid from one electrolytic unit. to the next, as Well as circulation of the liquid be tween the electrolyzer and the corresponding reducer; this is accomplished through the pipe D. It may also be desirable to circulate the liquid Within the reducer; this may be done through the pipe 12, which is so arranged that the overflow from the trougl'i 11 will be conducted into the bottom or the reducer, so that any gas in solution may act on the constituents in the liquid in the lower portion of the reducer, capable of acting on it. It may be desirable at times to heat the liquid; this may be done by the steam coil 13, in the lower portion oi? the reducer, or by heating the gas introduced in the upper portion, or both.

It is desirable to maintain quite a pool of the liquid in each reducer so that the gas, especially sulfur dioxid, may have ample time for effective reduction before the liquid is again introduced into the elcctrol vzer. The reaction between sulfur dioxid and ferric salts is quite slow in cold solutions; it is more rapid in heated solutons; in any case it is an important factor in satisfactory reduction. It is for this reason, among others, that the reducing chambers should be fairly large and that a large volume of solution should be continuously under the action of the s. it is believed, in general, that Within reasonable limits, the larger the pool of liquid in the reducers, the more satisfactory the entire operation Wlll be. It is also desirable to maintain a rapid flow of the liquid through the electrolyzers: this is preferably done by maintaining a large volume of the liquid in circulation, and the flow arranged so that the effluent liquid from the electrolyzers shall not contain more than 0.25% ferric iron, and preferably less. In order to get the best results from the rapid flow of the liquid the electrodes are preferably arranged so as to give the electrolyte a sinuous flow through the clectrolyzer. This gives effective deposition of the copper and also effective depolarization, and, both tie dcpolarization in the electrolyzer, and the reduction in the reducer, are made more effective by heating the solutions. It is, therefore, desirable to Work With heated rather than with cold solutions.

The operation of the apparatus may be best briefly described by referring more particularly to Fig. 3, although having in mind also Figs. 1 and 2.

The stream of copper solution, containing the iron presumably all, or nearly all, in the ferrous condition, is flowed at the required rate from the copper solution tanks into the reducing chamber No. 1 and into the electrolyzers No. 1 and No. 2. This is also the rate, of course, at which the solution is progressively advanced. The gas from the S0 generator is introduced, by means of the exhauster acting on the last cell, into reducer No. 1. The liquid in the reducer is treated with the gas confined over' it, as already described, and the sprayers spray or elevate a considerable portion of the liquid into the trough 11 which creates a flow of liquid to and from the electrolyzers. The reduced solution, issuing from the reducer through the pipe A, flows into the electrolyzers 1 and 2, and back again through the pipes B and C, while a portion of the stream is advanced to the next electrolytic unit. The stream of liquid flowing in the closed circuit between the reducer N o. 1 and the electrolyzers No. 1 and No. 2, is regulated, preferably, so that the efliuent liquid from theelectrolyzer will not contain over 0.25% ferric iron. If, for example, the infiowing liquid contains 3.0% copper, and it is desired to remove 1.0% in the first electrolytic unit, and if, during the deposition of 0.125% copper, 0.25% ferric iron is formed, it would have to pass through the closed circuit eight times before it is passed on to the next, and four times in passing through the second and third electrolytic units if it is desired to deposit 0.5% copper in each unit, so that the solution may be returned to the leaching vats containing 1.0% copper. Only experimenting, for each particular condition, will determine the best degree of impoverishment of the copper in the solution before returning it to the ore.

Again, suppose that each electrolyzer has a capacity of 1000 lbs. of copper per day of 24 hours. This would indicate an approximate fiow of liquid of 2 tons per hour. If the reducing chamber is, say, 10x20 feet, and the liquid 5 feet deep, it would contain about 30 tons of solution. If the flow for one electrolyzer is at the rate of 2 tons per hour, the average time of gas treatment in the reducer would be 15 hours, or, for 2 electrolyzers, as shown, 7.5 hours, etc. which will usually be an abundance of time for absorption and reduction. It may be much less. The best actual time for gasation of the liquid can only be determined by experiment.

'It is preferred to bring the richest gas in contact with the richest and most nearly neutral solution, so as not to give the ferric salts much of a chance to accumulate, or to be formed more rapidly than they can be reduced. It is for this reason that the rich gas from the S0 generator is preferably introduced into the first reducer. The flow of either gas or liquid could, of course, be in the opposite direction. The exhauster communicates with the last reducer, and before the gas is allowed to escape, the excess sulfur dioxid from the reducers is forced through a scrubbing tower, and absorbed by fresh solutions from the leaching vats. The amount of suction can be regulated by the speed of the exhauster, and there should always be at least a slight suction inwardly in all the reducers, so that none of the gas can escape and vitiate the atmosphere in the vicinity of the reducers.

The apparatus permits of the regeneration of a considerable amount of acid. Whether the sulfur dioxid acts as a depolarizer or reducer, as shown by the following equations, at least 3 lbs. of acid are regenerated per lb. of copper deposited.

1. CuSO,+SO. .+2I-I O-l-electrolysis:

Cu+2H,SO,,

3. SO,+211 O+electr0lysis:H SO +2I-I,'

but this reaction is undesirable, and the increased acid would be obtained at the expense of cathode efliciency.

Time and temperature are important factors in reducing ferric salts with sulphur dioxid. The ordinary way of showering the copper solution down through a scrubbing tower against an ascending stream of the gas, gives only momentary contact, and hence the reaction is very incomplete. It is quite ineffective with acid solutions, and acid is regenerated as soon as copper deposition begins. In the present practical application of the gas to copper solutions, so far as I am aware, it is not usual to attempt reduction in series, between the electroly zers. Manifestly, the momentary contact with the gas, makes such a procedure too ineffective for practical application. It is evident, with my apparatus, that the reduction may go continuously and simultaneously with the electrolysis, and that the copper solution may at all times be charged with a consider able proportion of the sulphur dioxid, and suflicient time can be allowed in the reducing chambers to make the reduction com plete, or quite nearly so.

I claim:

1. ln electrolytic apparatus, an electrolyzer, a closed chamber communicating with the electrolyzer and adapted to contain a pool of a liquid and to confine a gas over the liquid and having means for treating the liquid with the gas confined over it by mixing the gas and the liquid within the chamber, and means for circulating the liquid between the electrolyzer and the closed chamber.

2. In electrolytic apparatus, an electrolyzer, a reducing chamber communicating with the clectrolyzer and adapted to treat the electrolyte with a gas confined over it, and means arranged for withdrawing the electrolyte from the reducing chamber from a higher level than the quiescent surface of the electrolyte.

In electrolytic apparatus, an electrolyzer ,a gasing chamber adapted to contain a pool of a liquid and to confine a gas over the liquid and having a gas inlet and a gas outlet and having a liquid inlet and a liquid outlet communicating with the electrolyzer, means within the chamber for spraying the liquid into the gas confined over it, and means for causing a flow of liquid from the gasing chamber to the electrolyzer and from the electrolyzer to the gasing chamber.

4. In electrolytic apparatus, an electrolyzer, a gasing chamber adapted to contain a pool of a liquid and toconfine a gas over the liquid and having a gas inlet and a gas outlet and a liquid inlet and a liquid outlet, means for treating the liquid of the pool with the gas confined over it, means for causing a flow of gas over the pool, and means for causing a flow of liquid from the gasing chamber to the electrolyzer and from the electrolyzer to the gasing chamber.

In electrolytic apparatus, an electrolyzer, a gasing chamber communicating with the electrolyzer and adapted to contain a pool of a liquid in its lower portion and to confine a gas over the pool in its upper portion, rotary means within the chamber for spraying the liquid in the lower portion into the gas in the upper portion, means for maintaining a flow of gas through the gasing chamber, and means for causing a flow of liquid from the gasing chamber to the electrolyzer and from the electrolyzer to the gasing chamber.

6. In electrolytic apparatus, a series of electrolytic units each consisting of an electrolyzer and a gasing chamber communicating with the electrolyzer, means for introducing a gas into one gasing chamber of the series and advancing it progressively to the next of the series, means for confining a pool of electrolyte in the gasing chamber, means for treating the electrolyte in the pool with the gas confined over it, means for circulating a portion or" the electrolyte in a closed circuit between the electrolyzer and the gasing chamber, and means for progressively advancing a portion or" the electrolyte from one electrolytic unit to the next of the series,

7. In electrolytic apparatus, a series oi electrolytic units consisting of an electrolyzer and a gasingchamber communicating with the electrolyzer, a gas generator communicating with thegasing'chamber, means arranged for treating the electrolyte with the gas in the gasing chamber, means for circulating a portion of the electrolyte in a closed circuit between the electrolyzer and the gasing chamber, and means for progressively advancing a portion of the electrolyte from one electrolytic unit to the next of the series.

8. In electrolytic apparatus, a series oi electrolytic units each consisting of an electrolyz-er and a gasing chamber communicating with the electrolyzer, said gasing chambers being adapted to contain a pool of the electrolyte and to confine a gas over the pool, means arranged for treating the electrolyte with the gas, means for eXhausting the excess gas from one gasing chamber of the series and passing it on to the next, and means for progressively advancing the electrolyte from one electrolytic unit to the next. 7

9. In electrolytic apparatus, a series of electrolytic units each consisting of an electrolyzer'and a gasing chamber communicating with the electrolyzer, a gas generator communicating with the gasing chamber, and means arranged in connection with the gasing chamber for treating a pool of the electrolyte with-agas confined over it.

10. In electrolytic apparatus a number of electrolyzers arranged in series, a number oi gasing chambers adapted to contain a pool of the electrolyte and to confine a gas over the electrolyte of the pool corresponding with the electrolyzers, means for passing a gas through the series of gasing chambers, means for circulating a portion of the electrolyte in a closed circuit between the respective gasing chambers and the respective electrolyzers, and means for progressively advancing a portion of the electrolyte through the series of electrolyzers and reducing chambers.

11. In electrolytic apparatus, a number of electrolyzers arranged in series, a number of gasing chambers arranged in series which are adapted to contain a pool of the electrolyte and to confine a gas over the pool, means for passing a gas through the gasing chambers, means for treating the electrolyte in the respective gasing chambers with the gas, and means for progres sively advancing the electrolyte through the 1igespective electrolyzers and gasing chamers.

12. In electrolytic apparatus, an electrolyzer, a gasing chamber communicating with the electrolyzer and adapted to contain a pool of the liquid and to confine a gas over the liquid and having means for treating the liquid with the gas confined over it, means for circulating the liquid between the electrolyzer and the gasing chamber, means for circulating the liquid within the gasing chamber, and means for electrolyzing the liquid.

13. In electrolytic apparatus having a gasing chamber adapted for spraying the electrolyte into a gas confined over it, means for withdrawing the gassed electrolyte from a higher level than the quiescent surface of the electrolyte in the gasing chamber.

14:. In electrolytic apparatus having a gasing chamber communicating with an electrolyzer, means within the gasing chamber for elevating a portion of the electrolyte to a higher level than the quiescent surface of the electrolyte.

15. In electrolytic apparatus having an electrolyzer and a gasing chamber adapted to contain a pool of the electrolyte communicating with the electrolyzer, means for continuously treating the electrolyte in the pool with a gas confined over it.

16. In electrolytic apparatus, a series of electrolyzers, a series of gasing chambers communicating with the electrolyzers and adapted to contain a pool of the electrolyte and to confine a gas over the pool, means arranged for treating the electrolyte of the pool with the gas, means for progressively advancingthe electrolyte through the series of electrolyzers, means for progressively advancing the electrolyte through the series of gasing chambers to be treated by the gas, and means for progressively advancing the excess gas through the series of gasing chambers.

17. In electrolytic apparatus, an electrolyzer, a gasing chamber adapted to contain a pool of the electrolyte and to confine a gas over the pool and having a gas inlet and a gas outlet and an electrolyte inlet and an electrolyte outlet, means for treating the electrolyte of the pool with the gas, and means for causing a flow of electrolyte from the gasing chamber to the electrolyzer and from the electrolyzer to the gasing chamber.

18. In electrolytic apparatus, an electrolyzer, a gasing chamber adapted to contain a pool of the electrolyte and to confine a gas over the pool and having a gas inlet and a gas outlet and an electrolyte inlet and an electrolyte outlet, means for treating the electrolyte in the pool with a reducing gas, means for causing a fiow of reduced electrolyte from the gasing chamber to the electrolyzer and of oxidized electrolyte from the electrolyzer to the gasing chamber, and means arranged for regulating the flow of: electrolyte and the time of treatment so that the oxidation in the electrolyzer and the reduction in the gasing chamber may be maintained within predetermined limits.

19. In electrolytic apparatus, an electrolyzer, a gasing chamber adapted to contain a relatively large pool of the electrolyte under continuous treatment with a gas and adapted to confine a gas over the pool and having a gas inlet and a gas outlet and an electrolyte inlet and an electrolyte outlet, means for treating the electrolyte in the pool with a reducing gas, means for causing a flow of redu ed electrolyte from the gasing chamber to the electrolyzer and of oxidized electrolyte from the electrolyzer to the gasing chamber, and means arranged for regulating the flow of electrolyte and time of treatment so that the oxidation in the eleetrolyzer and the reduction in the gasing chamber may be maintained within predetermined limits.

WILLIAM E. GREENAWALT. 

